There is a need for high purity metal fluorides such as zirconium tetrafluoride, hafnium tetrafluoride and aluminum trifluoride as components for metal fluoride glass used in optical devices. Current commercial metal fluorides are not pure enough for all present day applications. Existing aqueous processes suffer from problems associated with dehydration of the hydrated metal fluorides. Current anhydrous synthetic routes involve complicated reactor designs.
In the literature article "The Reaction of Fluorine With Titanium, Zirconium and the Oxides of Titantium, Zirconium and Vanadium", by H. M. Haendler, S. F. Bartram, R. S. Becker, W. J. Bernard and S. W. Bukata, Journal of American Chemical Society, 1954, Vol. 76, pages 2177-2178, the reaction of zirconium oxide with fluorine is briefly disclosed. No specific parameters or results are highlighted.
In a literature article "Synthesis of Iron-impurity Free ZrF.sub.4 " by T. Tatsuno, Materials Science Forum. Vol. 19-20, 1987, pages 181-186, zirconium oxide is physically mixed with zirconium tetrafluoride prior to sublimation of zirconium tetrafluoride. The resulting sublimed zirconium tetrafluoride has a higher purity then sublimed zirconium tetrafluoride that has not been mixed with zirconium oxide.
In a literature article "Processing and Purification Techniques of Heavy Metal Fluoride Glass" by M. Robinson, Journal of Crystal Growth, 1986, Vol. 75, pages 184-194, a discussion of the problems of producing heavy metal fluoride glass using metal fluorides is set forth. Although sublimation and distillation are identified, the existing drawbacks and high impurity, levels despite such purification techniques, are highlighted.
U.S. Pat. No. 4,578,252 discloses an attempt to produce high purity metal fluorides using a combination of vaporization and electrolytic separation procedures.
In an article "Advances in Chemical Vapor Purification" by R. C. Folweiler and B. C. Farnsworth, extended abstracts, 5th International Symposium on Halide Glasses, Shizuoka Japan, May 1988, pages 533-537, techniques for production of high purity metal fluorides using advanced chemical vapor purification are set forth. However, as described in the conclusion the products were not suitable for ultra low loss optical fiber although they are suitable for high quality glass materials.
U.S. Pat. No. 4.652.438 describes a process for chemical vapor purification of materials for metal fluorides. The process includes reacting metal with a halide, isolating the metal containing compound and then reacting the metal containing compound with a fluorinating agent.
In a literature article by J. A. Sommers and V. Q. Perkins entitled "Research and Development for Commercial Production of High Purity Zirconium Tetrafluoride and Hafnium Tetrafluoride", extended abstracts, 5th International Symposium on Halide Glasses, Shizuoka Japan, May 1988, pages 169-173. A process is described for producing high purity metal fluorides involving the recrystallization of oxychloride from sublimed chloride with the addition of aqueous hydrogen fluoride to the oxychloride crystals to form zirconium tetrafluoride monohydrate and drying of the resulting monohydrate wet cake. A step of dehydration in flowing hydrogen fluoride yields the anhydrous product with low levels of contaminate metals.
In an article reported in Chemical Abstracts 1987. Vol. 107, Article 157676A by K. Fujiura, et al. the manufacture of high purity zirconium tetrafluoride is described. This is prepared by reacting zirconium tetrabromide with a gaseous fluorine-containing agent. Similar technology was reported by the same authors in extended abstracts 5th International Symposium on Halide Glasses at Shizuoka Japan, May 1988, pages 174-179 in an article entitled "Synthesis of High Purity Zirconium Tetrafluoride By Chemical Vapor Deposition".
An article by P. G. Devillebichot entitled "Zirconium As a Raw Material For Special Glasses", appearing in Glass Technology, 1983. Vol. 24(3}, pages 139-142 describes the preparation of zirconium tetrafluoride for special glasses using various reactions requiring the intermediate ammonium fluorozirconate.
All the techniques identified above suffer from complexity and resulting metal fluorides which still do not meet the demanding high standards for fiber optics and other high performance glass incorporating technologies. Appropriate metal fluorides which meet or exceed present demand standards have been achieved by the present invention which is set forth below.